Unable to mock `fs`

[rozele]

From my TypeScript class, I call:

import * as fs from "fs";
...
fs.writeFileSync(...);

In my tests, I call:

import * as fs from "fs";
import { ImportMock } from "ts-mock-imports";
...
ImportMock.mockFunction(fs, "writeFileSync");

When the test runs, the fs.writeFileSync function is not mocked.

[EmandM]

The way you are importing fs into your TypeScript class is incompatible with the ImportMock way of mocking out dependencies. ImportMock uses the module object as a stable point of reference in order to swap out real dependencies for fake dependencies. Instead of importing the entire module object into your class, instead directly import the functions you are using.

In your TypeScript class:

import { writeFileSync } from 'fs';
...
writeFileSync(...);

Now your test above should work as expected

[rozele]

It's strange, because ts-mock-imports seems to work as expected for other modules that I mock that also use import * as foo from "foo".

[rozele]

The other strange thing is your fix only seems to work if I run tests using mocha, but not ts-mocha.

[kkorus]

@rozele Can you show how you mock import * as foo from "foo"

My TypeScript class imports JavaScrilt file like:

// config.js
module.exports = { someConfig: 5 }


// mytypescript.ts
import * as config from 'config' 

and I need to find a way to mock it.